Conventionally, a motor including a stator formed of a molded resin body is often used in washing machines having a vertical rotation axis and in which motive power of the motor is transmitted to a washing/spin-drying tank and an agitator via belts, pulleys, and gears (See Patent Literature (PTL) 1, for example).
FIG. 7 is a cross-sectional view of a schematic structure of a conventional washing machine. As illustrated in FIG. 7, conventional washing machine 40 includes: washing/spin-drying tank 41; agitator 42 provided in a bottom surface of washing/spin-drying tank 41; and water tank 43 provided outside of washing/spin-drying tank 41 and agitator 42. Clutch device 44 is attached to a bottom surface of water tank 43. By connecting motor 45 and clutch device 44 by belt 46, a rotating force of motor 45 is transmitted to agitator 42 and washing/spin-drying tank 41 via clutch device 44. Here, clutch device 44 switches transmission of the rotating force of motor 45 to agitator 42 during washing and to washing/spin-drying tank 41 during spin-drying.
Next, a structure of motor 45 used in aforementioned conventional washing machine is described with reference to FIG. 8.
FIG. 8 is a perspective view of a schematic appearance of a motor used in a conventional washing machine. An outer hull of motor 45 is formed of molded resin body 54, and is fixed to the bottom surface of water tank 43 illustrated in FIG. 7 via fixing portions 55 integrally molded with molded resin body 54. Furthermore, power supply terminal 56 for supplying power to motor 45 is provided to molded resin body 54, and thus supplying power to power supply terminal 56 causes motor rotation shaft 64 to rotate. Normally, a pulley (not illustrated) is attached to motor rotation shaft 64, and the rotating force is transmitted to clutch device 44 via belt 46 illustrated in FIG. 7.
For motors of this type, there is a demand to reduce temperature rise value, improve efficiency, and reduce costs of the motor. When carrying out performance enhancement such as reducing the temperature rise value and improving efficiency in aforementioned conventional motor 45, improving heat-dissipation capability is effective. As such, together with improving motor efficiency, efforts have been made to increase heat-dissipation area by increasing axial direction length and radial direction dimension of motor 45.
Furthermore, structures have been disclosed which improve heat-dissipation capability and performance of a motor while suppressing an increase in size of the motor (see PTL 2 and PTL 3).
However, improving heat-dissipation capability by increasing the axial direction length and the radial direction dimension increases a volume of motor 45, and thus cost increases. In addition, since dimensions of motor 45 can only be changed within a range defined by dimensional restrictions of a bottom surface of washing machine 40 and dimensional restrictions of clutch device 44 and water tank 43 illustrated in FIG. 7, there is a limit to the improvement of the performance of motor 45.
On the other hand, using the structures disclosed in PTL 2 and PTL 3 entails less cost increase and dimensional restrictions compared to when only the increasing the axial direction length and radial direction dimension of the motor is carried out. However, since they are merely structures provided with a recessed and projecting shape in an axial-direction end surface of the molded resin body, it is necessary to increase a height of projections to further increase the heat-dissipation area in order to further improve performance. Therefore, within the range defined by the aforementioned dimensional restrictions, there is a limit to the improvement of heat-dissipation capability.